1. Field of the Invention
The present invention relates generally to a ball screw, and more particularly, to an internal circulation ball screw.
2. Description of the Related Art
A generic ball screw includes two types—external circulation ball screw and internal circulation ball screw. In the external circulation ball screw, a guiding member is mounted to a nut for guiding circulative movement of rolling members. Generally speaking, the external circulation ball screw is applicable while the pitch is longer and the nut is bigger relatively. As for the internal circulation ball screw, a circulation member is additionally mounted inside the nut to allow circulative movement of the rolling members inside the nut, so the internal circulation ball screw is applicable while the pitch is shorter and the nut is smaller relatively.
The conventional internal circulation ball screw includes a circulation member, which is usually linearly arranged, as shown in FIGS. 1-2. However, the circulation member 1 having circulation channels 2 linearly arranged may have the following problem. As shown in FIG. 1, when the circulation member 1 works with a ball screw having shorter stroke, it is necessary to apply cross-thread design to the internal circulation ball screw to prevent the circulation member 1 from damage resulting from excessively thin walls of the circulation channels. However, the cross-thread design will result in that the nut is too long and the ineffective threads become more. In addition, the pitch between the adjacent circulation channels 4 provided by the circulation member 3 shown in FIG. 2 for the rolling members to cross the peak of the thread is too small and the walls of the circulation channels 4 are thin, so the circulation member 3 is subject to damage.